BIRMINGHAM, Alabama - Jefferson and Shelby counties are under an orange air quality alert today, only the second time this year that the Code Orange has been issued.

The alert, issued by The Alabama Department of Environmental Management, means ground-level ozone levels could be irritating for sensitive groups, including children and people with asthma. The only other such alert was issued for Tuesday, July 30, according to the National Weather Service.

There were 11 Code Orange alerts issues in 2012. Jessica Chace, a NWS meteorologist, said the rain has helped keep the air quality alerts at bay this year.

A typical summer weather pattern has high
pressure sitting over the area, which causes a buildup of pollutants that lead to the formation of ozone, said Matthew Lacke, Meteorologist with the Jefferson County Department of Health and Environmental Health Services in an e-mail to AL.com.

Ozone is produced from the chemical reaction created by intense sunlight between volatile organic compounds, which come from vehicle exhaust, paint, solvents, and natural sources, and nitrogen oxides, which come from combustion sources, explains Lacke.

"The fact that we have had cooler temperatures and more cloud cover than usual
have played significant roles in keeping the concentrations of ozone
down," said Lacke. "There are also non-weather factors that have contributed to the
overall downward trend in ozone over time."